System for managing feedback

Abstract

Feedback detection, adaptive notch filtering, and gain adjustment are combined for managing feedback. Feedback detection includes detection of short term and long term spectral peaks and assessing their magnitude, shape, rate of growth, and power concentration ratio. A plurality of notch filters are available and are allocated according to the spectral magnitude of the feedback detected. Wide band gain adjustment supplements the notch filters.

1. A system for managing audio feedback, said system comprising:
 a feedback detector, including a short peak detector and a long peak detector; 
 at least two adaptive notch filters coupled to said feedback detector; and 
 a control circuit coupled to said feedback detector and to said at least two adaptive notch filters for setting the depth, width, and frequency of at least one of said adaptive notch filters in accordance with data from said feedback detector. 
 
     
     
       2. The system as set forth in  claim 1  wherein said short peak detector evaluates magnitude and shape for detecting a spectral peak. 
     
     
       3. The system as set forth in  claim 2  wherein said short peak detector evaluates relative height for detecting a peak. 
     
     
       4. The system as set forth in  claim 1  wherein said short peak detector operates in frequency domain and sets a threshold as a fraction of the difference between the maximum spectral magnitude and the minimum spectral magnitude in a frame of data. 
     
     
       5. The system as set forth in  claim 4  wherein said feedback detector operates on a plurality of frames of data and sets said threshold for each frame. 
     
     
       6. The system as set forth in  claim 1  wherein said control circuit allocates adaptive notch filters in descending order of magnitude of peaks identified by said feedback detector. 
     
     
       7. The system as set forth in  claim 1  wherein said control circuit reduces the threshold for feedback detection in said feedback detector after said feedback detector identifies a peak as feedback. 
     
     
       8. The system as set forth in  claim 1  wherein said control circuit initially increases the depth of the notch of said at least one adaptive notch filter after allocating said at least one adaptive notch filter to reduce feedback. 
     
     
       9. The system as set forth in  claim 8  wherein said control circuit gradually reduces the depth of the notch of said at least one adaptive notch filter after reducing feedback. 
     
     
       10. The system as set forth in  claim 1  and further including a gain adjust circuit coupled to said notch filters. 
     
     
       11. The system as set forth in  claim 10  wherein the gain adjust circuit gradually decreases system gain in a frequency band where feedback remains even after application of a notch filter. 
     
     
       12. In a hearing aid having a speaker and a microphone, the improvement comprising a system for managing feedback from said speaker to said microphone, wherein said system includes:
 a feedback detector coupled to said microphone, said feedback detector including a short peak detector and a long peak detector; 
 at least two adaptive notch filters coupled to said feedback detector; and 
 a control circuit coupled to said feedback detector and to said at least two adaptive notch filters for setting the depth, width, and frequency of at least one of said adaptive notch filters in accordance with data from said feedback detector. 
 
     
     
       13. The hearing aid as set forth in  claim 12  wherein said system further includes a gain adjust circuit coupled between said notch filters and said speaker. 
     
     
       14. The hearing aid as set forth in  claim 13  wherein the gain adjust circuit gradually decreases system gain in a frequency band where feedback remains even after application of a notch filter.